As the functional constituent members of metabolism involve a disintegration of the nitrogen-free atom groups, the functional self-regulation must necessarily furnish in sufficient quantity and in proper form the carbon, hydrogen and oxygen atoms, which have been removed in the production of carbon dioxide and water. This is accomplished, as is well known, by the food and the intake of oxygen. It is of importance to the maintenance of living substance that after every functional activity it is as soon as possible again capable of reaction. Therefore, it is absolutely necessary that this material is in the proper place, where building up is essential, and is at the same time constantly in proper form. Indeed, the restitution of the original state follows under favorable conditions with lightning rapidity, although varying in different forms of living substance. This occurs in the nerve in an extremely short time. From this it might be supposed that the living system by accumulating a store of the necessary compensation substances in suitable form, had made itself independent to a certain degree of the frequently varying supply of material obtained from the medium. This may be held as the proper view, first with regard to compensation substances. The fact that living organisms can under some conditions remain for a lengthened period in a state of starvation, without losing their capability of activity, can only be explained by the presence of a great quantity of reserve supplies of compensation substances. In the course of work in the laboratory every physiologist has become acquainted with the fact that frogs which have been kept without food for a year, although much reduced in weight, are still capable of some muscular activity. [Illustration: A B Fig. 12. Motor ganglia cells from the spinal cord of the frog. A--In normal state. B--After an asphyxiation lasting 8 to 9 hours. (After _Gordon Holmes_.)] [Illustration: Fig. 13 _Paramecium aurelia._ A--In normal state. B--In a state of starvation.]